This application relates to turbine engine blades. More particularly, the application relates to thermal barrier coatings and cooling holes for use with turbine engine blades.
High heat loads exist between the tip of a turbine engine blade and its shroud. The tip temperature for a high pressure turbine blade, for example, can be a limiting factor in the design and operation of a turbine engine. As a result, efforts are made to reduce the temperatures at the blade tip.
One prior art tip cooling approach uses a thermal barrier coating at the tip to reduce the heat flux at the tip. Another approach provides tip cooling holes that apply a film of cooling fluid in the vicinity of the tip. Another approach is to provide machined pockets at the tip to reduce heat transfer in the area, retain the cooling flows and reduce the volume of metal at the tip that needs to be cooled. One or more of these cooling approaches may be applied to a particular blade to achieve lower blade tip temperatures.
Despite the use of the approaches described above, undesirably high tip temperatures exist. Heat loads within the pocket are typically higher than desired. External surfaces are typically covered with thermal barrier coatings to reduce the heat flux. However, lower metal temperatures can be achieved by removing the thermal barrier coating at the tip, which forms a shelf that increases film effectiveness in the area. While this has been achieved in the prior art, it is unknown what techniques have been employed to provide the shelf. What is needed is a further reduction in blade tip temperature.